On the environmental suitability of high- and low-enthalpy geothermal systems

•Life cycle assessment of power generation using high-enthalpy geothermal resources.•Life cycle assessment of heat generation using low-enthalpy geothermal resources.•Life-cycle inventory data, energy balances and environmental impacts.•Geothermal electricity is a promising alternative to fossil electricity.•Suitable geothermal heat systems require eco-friendly electrical grids.

This article addresses the life cycle assessment of (i) power generation in a binary-cycle power plant using high-enthalpy geothermal resources, and (ii) heat generation in a closed-loop geothermal heat pump system using low-enthalpy resources. For the geothermal power system, production and injection wells show a high contribution to the environmental impacts, mainly due to activities such as drilling and casing. Power plant operation is also identified as an important source of impact because of working fluid losses. A favourable life-cycle energy balance is estimated for this system. Furthermore, when compared to fossil electricity, geothermal electricity is generally found to be a promising alternative. For the geothermal heat system, the electricity demands for heat generation and use are the main sources of impact. An unfavourable life-cycle energy performance is predicted for this system. When compared to fossil heat, the environmental suitability of geothermal heat highly depends on the availability of eco-friendly electrical grids.